The benefits of variable valve timing to control internal combustion engine cylinder intake charge are well-established. It is further known that backflow may be prevented in variable valve timing applications through placement of check valves, such as reed valves, in the engine intake manifold. Still further, active intake charge throttling for each cylinder has been proposed using a butterfly or rotary cylinder inlet valve. The control under such mechanizations, such as that described in U.S. Pat. No. 5,372,108, requires instantaneous valve timing information. Crankshaft and camshaft phasing diagnostics may further be provided through the benefit of precise valve event timing. Absolute internal combustion engine camshaft position information, which may only be available at one camshaft angular position for each engine cycle, may be used to derive a rough approximation of valve timing in variable valve timing systems. Camshaft position sensor signal processing delays and engine speed transients can significantly reduce the accuracy of such a derivation. Indeed, the inaccuracy of the derivation may disqualify it for use in many engine control and diagnostic applications.
An approach to determining valve timing in variable valve timing engine applications with sufficient precision for application in engine control and diagnostics is therefore desirable. It is further desired that such an approach add minimal cost and complexity to current variable valve timing control and diagnostic applications.